Reuhs B L, Geller D P, Kim J S, Fox J E, Kolli V S, Pueppke S G
Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602-4712, USA.
Appl Environ Microbiol. 1998 Dec;64(12):4930-8. doi: 10.1128/AEM.64.12.4930-4938.1998.
Lipopolysaccharides (LPS) and capsular polysaccharides (K antigens) may influence the interaction of rhizobia with their specific hosts; therefore, we conducted a comparative analysis of Sinorhizobium fredii and Sinorhizobium meliloti, which are genetically related, yet symbiotically distinct, nitrogen-fixing microsymbionts of legumes. We found that both species typically produce strain-specific K antigens that consist of 3-deoxy-D-manno-2-octulosonic acid (Kdo), or other 1-carboxy-2-keto-3-deoxy sugars (such as sialic acid), and hexoses. The K antigens of each strain are distinguished by glycosyl composition, anomeric configuration, acetylation, and molecular weight distribution. One consistent difference between the K antigens of S. fredii and those of S. meliloti is the presence of N-acetyl groups in the polysaccharides of the latter. In contrast to the K antigens, the LPS of Sinorhizobium spp. are major common antigens. Rough (R) LPS is the predominant form of LPS produced by cultured cells, and some strains release almost no detectable smooth (S) LPS upon extraction. Sinorhizobium spp. are delineated into two major RLPS core serogroups, which do not correspond to species (i.e., host range). The O antigens of the SLPS, when present, have similar degrees of polymerization and appear to be structurally conserved throughout the genus. Interestingly, one strain was found to be distinct from all others: S. fredii HH303 produces a unique K antigen, which contains galacturonic acid and rhamnose, and the RLPS did not fall into either of the RLPS core serogroups. The results of this study indicate that the conserved S- and RLPS of Sinorhizobium spp. lack the structural information necessary to influence host specificity, whereas the variable K antigens may affect strain-cultivar interactions.
脂多糖（LPS）和荚膜多糖（K抗原）可能会影响根瘤菌与其特定宿主的相互作用；因此，我们对费氏中华根瘤菌和苜蓿中华根瘤菌进行了比较分析，这两种根瘤菌在遗传上相关，但在共生方面存在差异，它们是豆科植物的固氮微共生体。我们发现这两个物种通常都会产生菌株特异性的K抗原，这些抗原由3-脱氧-D-甘露-2-辛酮糖酸（Kdo）或其他1-羧基-2-酮-3-脱氧糖（如唾液酸）和己糖组成。每个菌株的K抗原通过糖基组成、异头构型、乙酰化和分子量分布来区分。费氏中华根瘤菌和苜蓿中华根瘤菌的K抗原之间一个一致的差异是后者的多糖中存在N-乙酰基。与K抗原不同，中华根瘤菌属的LPS是主要的共同抗原。粗糙型（R）LPS是培养细胞产生的LPS的主要形式，一些菌株在提取时几乎不释放可检测到的光滑型（S）LPS。中华根瘤菌属被分为两个主要的R-LPS核心血清群，这与物种（即宿主范围）不对应。当存在S-LPS时，其O抗原具有相似的聚合度，并且在整个属中结构似乎是保守的。有趣的是，发现一个菌株与其他所有菌株不同：费氏中华根瘤菌HH303产生一种独特的K抗原，其中含有半乳糖醛酸和鼠李糖，并且该R-LPS不属于任何一个R-LPS核心血清群。这项研究的结果表明，中华根瘤菌属保守的S-和R-LPS缺乏影响宿主特异性所需的结构信息，而可变的K抗原可能会影响菌株-品种间的相互作用。
